"Dutch Roll"

[Bootlegger]

  What causes "dutch roll", and do control line models suffer from it?  A deceased friend flew free flight models and I would hear him say the model suffered from "Dutch Roll", but I don't remember him saying what it was or what caused it..

       Thanks a lot...

[Dan McEntee]

   I have heard the term "dutch roll" used to describe a slight lateral yawing of an airplane, usually caused by not enough vertical stab or fuselage area. V tailed airplanes tend to do this and I have heard of the Beech Bonanza having a tendency to dutch roll a bit. I used to fly R/C sailplanes quite a bit, and the Airtronics Aquila would dutch roll when you got flying pretty fast in a shallow dive or trying to come down from altitude for a precision landing. Control line models, just by their nature of how they fly, probably would not exhibit any habits like I described. All the engineers in the forum will be able to add more science to the discussion, but that is the way I have heard it explained to me.
  Type at you later,
   Dan McEntee

[Tim Wescott]

Too much vertical stabilizer for the dihedral and the plane will go into an ever-tightening spiral.

Too little, and the plane will yaw, then roll in the direction of the yaw, then the stab will catch up and yaw it the other way -- and repeat.

Constrain the plane in yaw and roll by tying a string to a wingtip and letting it whirl around a point, and you won't see this to any great degree.

[Howard Rush]

An interesting piece by Jan Roskam, a famous aero professor who is Dutch: https://books.google.com/books?id=rBksUk40jlEC&pg=PA86&lpg=PA86&dq=dutch+roll+roskam&source=bl&ots=oNiUd96TlJ&sig=BeokZK79bRr-B3RQKoXaJYZmhmQ&hl=en&sa=X&ved=0ahUKEwigmZ_Uq7XMAhVX5GMKHRiLAiMQ6AEIHTAA#v=onepage&q=dutch%20roll%20roskam&f=false

A sorta imperfect piece from Wikipedia: https://en.wikipedia.org/wiki/Dutch_roll

Linearized conventional, rigid airplane lateral-directional dynamics are fourth order (is that the right term?) with two first-order modes and one second-order mode: Dutch roll.  Do control line airplanes have Dutch roll?  Good question.  The lines get into the act, so who knows? 

Dutch roll is a problem particularly with airplanes that have swept wings and fly fast.  A big enough vertical stabilizer will fix it, but can cause other trouble.  A better fix is a Rabe-rudder sort of thing that moves the rudder as a function of yaw rate (and other stuff on more recent airplanes). 

[Tim Wescott]

Linearized conventional, rigid airplane lateral-directional dynamics are fourth order (is that the right term?) with two first-order modes and one second-order mode: Dutch roll.

Four?  Hmm.

Yes, a fourth-order system (at least a linear one) has four modes (or eigenvalues, or poles).  I don't think that you can, in general, talk about a non-linear system having modes as such, but if there's four integrators in play then it's a 4th-order system.

  Do control line airplanes have Dutch roll?  Good question.  The lines get into the act, so who knows? 

Good question indeed -- I think that the characteristic frequency of the dutch roll would be so high that it would have a sound, and that sound would be "brrrrrraaaaaaAAAAAAP


BLAM".

Possibly followed by the sound of an engine thunking into something, and cursing.  (If I'm flying, maybe maniacal laughter instead of cursing -- I sometimes have atypical reactions to trauma).

Since there have been no reported cases of this phenomenon, I think we can assume that the behavior doesn't exist.

[dale gleason]

Bruno may shed some light on this phenomenon.

The 727 with its highly swept- back wing has negative stability with both its yaw dampers turned off...the third oscillation, if allowed to continue, will go inverted.

 One wing moving forward, relative to the other, will have more lift, relative to the other, so it "rises" relative to the other. But, its drag increases and so it retreats relative to the other, losing lift and "descends",  relative to the other. Side to side and up and down, it gets interesting very quickly.

When fuel was cheap, pilots in training practiced controlling Dutch Roll manually in the airplane up around  35000' at  high Mach numbers. In later years training was done in simulators, which proved more difficult to handle for some pilots, who broke out in hives and muttered things about Boeing engineers, so I've been told......   

     dg

[pat king]

I was told that the first KC 135 airplanes had problems with "Dutch Roll" and were modified to correct the problem.

Pat

[Paul Smith]

In Wichita one of our KC-135's Dutch-rolled in Cessna Field and burned to a crisp.  Some time around 1975.

The accepted cause was a simulated engine failure on takeoff that resulted in low speed/nose high attitude that turned in a Dutch-rolling descent into the ground (about a quarter-mile from my house).

I don't think this has any relation to any CL event.  It occurs on swept wing airplanes that get into unusual yaw conditions.

[Howard Rush]

Bruno may shed some light on this phenomenon.

The 727 with its highly swept- back wing has negative stability with both its yaw dampers turned off...the third oscillation, if allowed to continue, will go inverted.

 One wing moving forward, relative to the other, will have more lift, relative to the other, so it "rises" relative to the other. But, its drag increases and so it retreats relative to the other, losing lift and "descends",  relative to the other. Side to side and up and down, it gets interesting very quickly.

When fuel was cheap, pilots in training practiced controlling Dutch Roll manually in the airplane up around  35000' at  high Mach numbers. In later years training was done in simulators, which proved more difficult to handle for some pilots, who broke out in hives and muttered things about Boeing engineers, so I've been told......   

     dg

The tail on the 727 wasn't very far back and didn't have to be very big to counter an engine out, so Dutch roll was lightly damped.  It was indeed unstable at high altitude.  As I recall, the solution was to provide redundant yaw dampers.  If one failed, you'd go to a lower altitude.  The 727 could have had a larger vertical stabilizer, but that would have meant more drag, hence more fuel burn, which would have to have come out of pilot pay. 

[Tim Wescott]

I don't think this has any relation to any CL event.  It occurs on swept wing airplanes that get into unusual yaw conditions.

Also free-flight airplanes with exaggerated dihedral.

[Bootlegger]

    Ty, the cinnamon worked really well..

[Gerald Arana]

Gil, add  some cinnamon, no more problems.

And I like slivered almonds too! 

Jerry

[Steve Helmick]

Back in the '70's, one of Boeing's Free Flight guys, John Crosetto (and Strat-o-Bat, like Ted Fancher and later, myself) set up a small company making a molded foam HLG ("Hand Launched Glider", aka "Hurl Glider" or "Chuckie") with elliptical dihedral. They were sold in hobby and toy stores and flew fairly well, but tended to spin in, as Tim detailed. Perhaps you saw them, or even bought some?

Tired of the spinning (having been given some free samples), I cut the wing tips not quite through and added a little dihedral. I got an interesting result, "Dutch Roll". The wing appeared to slide side to side...not very efficient, but a very safe flight mode. Very good for flying in thermals, however.

A good HLG designer will build with too much fin area and carefully reduce fin area until the spinning stopped. I preferred going the other direction, and started with too little fin area, until this spanwise wiggle stopped. But I didn't really fly much HLG. My elbow didn't like flinging them that much, confirmed by years of bass fishing.    Steve

[WR Crane aka MrClean]

I've got a guy who brings Dutch Letters to our yearly flying get together.  Pretty buttery.

[Ted Fancher]

Bruno may shed some light on this phenomenon.

The 727 with its highly swept- back wing has negative stability with both its yaw dampers turned off...the third oscillation, if allowed to continue, will go inverted.

 One wing moving forward, relative to the other, will have more lift, relative to the other, so it "rises" relative to the other. But, its drag increases and so it retreats relative to the other, losing lift and "descends",  relative to the other. Side to side and up and down, it gets interesting very quickly.

When fuel was cheap, pilots in training practiced controlling Dutch Roll manually in the airplane up around  35000' at  high Mach numbers. In later years training was done in simulators, which proved more difficult to handle for some pilots, who broke out in hives and muttered things about Boeing engineers, so I've been told......   

     dg

Like Cap'n Gleason I was introduced to swept wing Dutch roll in a Boeing...a 707-720 in my case and we did, indeed, train in Dutch Roll management primarily intended to become necessary in the event of the loss of the single (IIRC) yaw damper installed on these earliest of Boeing swept wing air carrier types.

Less widely known was the flight attendants' (nee "Stewardesses') description of the airplane as the "Sauna wobble bus!"  The "wobble" referring to the constant "left and up, right and up, repeat until passengers cease vomiting" semi-restrained Dutch Roll action at the tail end of the passenger  cabin even with the yaw damper fully functional.  The sauna adjective referring to the lousy engine bleed air driven air conditioning system (especially on the ground at idle power...I can remember taxiing out for take off in long lines on hot humid midwest days in undershorts and T-shirts with a modesty blanket close at hand should a lady show up at the door!). 

I don't recall similar training when checking out on the dual yaw damper equipped 727 although I do recall the altitude restrictions in the limitations section of the AOM.  Probably wasn't stressed as hard due to the damper redundancy but don't quote me. 

Ted

[dale gleason]

I really enjoyed my stay on the 727. Howard had a lot to do with that. The Triple Seven was really nice, too. Howard again.

 A side note on 720 nicknames....I've been told at Eastern it was affectionately referred to as "Old Wobbly" .

dg

[Howard Rush]

I had little to do with the 727.  About all I did for the 777 was to help folks working on it get organized.

[dale gleason]

I wonder why it's called "Dutch" roll. Maybe a seafaring Dutchman used the phrase, "Yar she blows!" ?    dg

[FLOYD CARTER]

I don't know if it was Dutch Roll, but in a Lockheed 1011, I once got the rear-most seat.  In moderate turbulence, the entire fuselage was twisting!  Easy to see from my seat.

Floyd

[Kevin Ferguson]

I wonder why it's called "Dutch" roll. Maybe a seafaring Dutchman used the phrase, "Yar she blows!" ?    dg

It refers to the motion of a racing ice skater, rolling the body side-to-side as weight is transferred from one foot to the other...speed skating having evolved in holland, the gait/technique is known as the dutch roll.

[dale gleason]

Thank you! I believe that accurately describes the combination of "yaw" and "roll" once referred to as "Yar".

dg